Theory
3D Pythagoras and 3D trigonometry questions usually become two ordinary right-angled triangle questions.
Do not try to use every length in the 3D shape at once. First find the right triangle that sits on a face or across the base.
In a cuboid, the base diagonal is often found first using Pythagoras on the base rectangle.
After finding the base diagonal, combine it with the height to make a second right-angled triangle through the solid.
For an angle of elevation in a cuboid, the horizontal distance is often the base diagonal, not just one edge.
Higher note: draw the hidden triangle separately if the 3D diagram feels crowded.
Edexcel questions often award marks for the intermediate length, so show the base diagonal before the final answer.
Key ruleFind the hidden 2D right triangle first. In cuboids, base diagonal first, then space diagonal or angle.